1. Field of the Invention
The present invention relates generally to a ceramic pressure sensor or detector, and more particularly to a ceramic pressure sensor suitable for measuring or determining a pressure acting on a ceramic diaphragm with electrical resistors formed thereon, depending upon a variation in the resistance value of the resistors due to deformation or strain of the diaphragm in response to the pressure applied thereto.
2. Discussion of the Prior Art
There is known a pressure sensor of a type in which electrical resistors connected in a bridge configuration are integrally formed on a surface of a suitable deformable diaphragm or substrate. Deformation or strain of the diaphragm in response to a pressure applied thereto causes a change in the electrical output of the bridge circuit of the resistors, whereby the pressure acting on the diaphragm may be determined by the electrical signal produced by the bridge circuit. Examples of this type of pressure sensor have recently been proposed in SAE Reports 820319 and 860474, wherein the diaphragm is formed of a ceramic material.
In the pressure sensor employing such a ceramic diaphragm, a plurality of resistors 10 are integrally formed on one of opposite major surfaces of the ceramic diaphragm in the form of a thin film or sheet 12. The ceramic diaphragm 12 is retained within a bore of a cylindrical metallic housing 16, such that the diaphragm 12 is fixed at its outer circumferential portion by a ceramic support body 14 also accommodated in the metallic housing 16. The metallic housing 16 has an open end having an opening 18, through which the other major surface of the ceramic diaphragm 12 is exposed to an atmosphere in an external space. Thus, the ceramic diaphragm 12 having the integrally formed resistors 10 is exposed to a pressure of the external atmosphere introduced through the opening 18 at the open end of the metallic housing 16.
The pressure sensor constructed as described above is suitably used for measuring a pressure in a space exposed to a relatively high temperature. In this case, an electrical output of the resistors 10, representative of the pressure acting on the ceramic diaphragm 12, is likely to be influenced by an electromagnetic wave in the measuring space or environments. Thus, the measuring accuracy of the pressure sensor is deteriorated by such an electromagnetic disturbance.
For instance, where the pressure sensor is utilized for measuring the pressure within a cylinder bore of an internal combustion engine, i.e., for determining the combustion pressure of the engine, the electrical output of the sensor is affected by an electromagnetic wave or noise which occurs upon energization of ignition or spark plugs of the engine, whereby the pressure represented by the obtained electrical output of the pressure sensor includes a certain amount of error or deviation from the actual pressure in the cylinder bore.